RU2163524C1 - Method for preparing sand for making molds and cores with gypsum binder at producing castings of non-ferrous and precious metals - Google Patents

Abstract

FIELD: foundry. SUBSTANCE: method for preparing sand comprises steps of agitating sand ingredients and vacuum treatment of sand; simultaneously with vacuum treatment applying to sand ultrasonic oscillation field for 2-6 min. Combination of ultrasonic and vacuum treatment processes provides intensive separation of air bubbles from treated sand. EFFECT: enhanced rheological properties of sand and physico-mechanical characteristics of molds and cores. 1 tbl

Description

 The invention relates to the field of foundry and can be used for the manufacture of molds and cores on a gypsum binder in the production of castings from non-ferrous and precious alloys.

 At present, for this the most widely used is EN-TIOC - process / 1, 2 /. However, being highly specialized in the manufacture of jewelry, this method of forming from imported cristobalite-gypsum mixtures ("Supercast", "Santicast", "Ultravest" and others) or domestic dynamo-gypsum mixtures ("Jewelery - 1", "Jewelry - 2 ") does not provide the required manufacturing quality by investment casting (LWM) of large-sized complex art or engineering castings.

The closest in technical essence is the method of preparing ceramic molds and cores in the manufacture of castings from non-ferrous and precious alloys / 3 /. In accordance with the specified prototype in the preparation of a mixture having a composition, wt.%:
Gypsum - 10 ... 14
Dinas - 59 ... 63
Dusty sublimation of fireclay production - 3.7 ... 7.0
Alumochromophosphate binder - 0.003 ... 0.020
Water is the rest
carry out pre-treatment of an aqueous solution of aluminochromophosphate binder with nanosecond electromagnetic pulses, followed by mixing of the ingredients and vacuum treatment of the resulting suspension during vibration.

The known technical solution ensures the stability of the properties of the mixture and the manufacturability of the molding operation. However, the prototype has the following significant disadvantages:
- low efficiency of the vacuum treatment for the degassing of large volumes of slurry required in the manufacture of large-sized art or engineering castings, which leads to their increased rejection by influx;
- insufficient level of the rheological properties of the suspension for high-quality reproduction of its developed surface of complex profile investment models;
- an unsatisfactory complex of strength characteristics of molds and rods on a gypsum binder for investment casting of large-size castings by investment casting, which, as their mass increases, causes an increase in rejects by blockages;
- the formation of surface defects (sagging, blockages) on art and engineering castings increases the complexity of their cleaning and leads to irretrievable losses of non-ferrous and precious metals and alloys.

 The basis of the invention is the task of creating such a method of preparing a mixture that would ensure the formation of conditions for its effective degassing, improve the rheological properties of the suspension and the physico-mechanical characteristics of the molds and rods on a gypsum binder to improve the quality of production of art and machine-building castings from non-ferrous and precious alloys especially large and massive.

 This problem is solved in such a way that in the method of preparing a mixture for the manufacture of molds and rods on a gypsum binder in the manufacture of castings from non-ferrous and precious alloys, including mixing the ingredients of the mixture and its vacuum treatment, according to the invention, an ultrasonic field is applied to the mixture simultaneously with evacuation for 2 ... 6 minutes

 The combination of ultrasonic and vacuum treatment of the gypsum slurry provides for the intensive release of air bubbles from it, including those dissolved in an aqueous grinder, their coalescence and effective degassing of the mixture as a result of cavitation and acoustic flows initiated by an ultrasonic field in the liquid phase of the suspension. The process of degassing the mixture is also accelerated due to the resulting pressure drop in the gas bubble and discharge over the suspension. In this case, carrying out vacuum-ultrasonic treatment of the mixture for 2.6 minutes is optimal, since it is during this period of time that the viscosity of the hardening suspension increases to such values that air bubbles are still capable of moving and removing from the entire volume of the mixture. A further increase in processing time leads to the fact that the viscous forces begin to inhibit the process of degassing a suspension with a gypsum binder.

 The application of an ultrasonic field to the mixture provides an increase in its fluidity and solidification time required for high-quality manufacturing in investment casting technology of large-sized molds and rods on a gypsum binder. The indicated effect is achieved due to the ionization of the matrix and dispersion of its particles under the action of ultrasound. The resulting ions of the dissolved substances of the hardener are adsorbed on the gypsum particles and in a certain way block its interaction with water, increasing the suspension solidification time. Grinding particles of the solution causes a decrease in the viscosity of the suspension at a given filling and provides improved reproducibility of the configuration of complex models. The "liquefaction" of the caster also allows to increase the degree of filling of the suspension and thereby increase the strength and crack resistance of the molds and cores.

 Thus, the achieved effective degassing of the mixture, improved rheological properties and strength characteristics of molds and cores create conditions for improving the quality of production by investment casting of large-sized art or machine-building castings from non-ferrous and precious alloys.

 The proposed method of preparing a mixture for the manufacture of molds and cores on a gypsum binder in the manufacture of castings from non-ferrous and precious alloys is as follows.

 Prepare the grout mixture. Dry molding material is poured into it, which can be used as domestic mixtures on a gypsum binder: Jeweler - 1, Jeweler - 2, imported: Ultravest, Supercast, etc. Moreover, the best results for large casting gives the mixture proposed in the prototype. Then, the ingredients are mixed, followed by simultaneous evacuation and ultrasonic treatment of the suspension with gypsum binder for 2 ... 6 minutes. For this, a setup consisting of an ultrasonic generator, for example, grades UZG-22-10, UZG-8-01 / 22/4 /, a magnetostrictive transducer (PSM-15), and a bath, the bottom of which is a waveguide connected to the core of the transducer, can be used. . The bath is hermetically sealed with a lid, into which a rod with an impeller, driven by an electric motor, is installed through the sealing system to mix the ingredients of the mixture. The receiver and the vacuum pump are connected to the bath through the pipeline. Thus, by mixing the ingredients of the mixture in the bath, vacuum-ultrasonic treatment of the resulting suspension is carried out simultaneously. The ultrasonic bath is mounted on pins and can be rotated relative to the horizontal axis for pouring the prepared liquid-moving mixture into equipment (flasks, core boxes) in the manufacture of molds and rods on a gypsum binder.

 The suspension is treated at an ultrasound frequency of 22 ... 24 kHz and a power of 80 ... 100 W at the output of the generator, the residual air pressure in the bath is 1400 ... 2000 Pa.

 Vacuum-ultrasonic treatment lasting less than 2 minutes is ineffective, because it is not possible to remove air from large volumes of the suspension and significantly improve its technological properties.

 When processing for more than 6 minutes, an increase in the viscosity of the hardening liquid-moving mixture complicates its degassing. In particular, gas bubbles formed as a result of the cavitating action of ultrasound remain in suspension, providing castings for spills.

 The proposed method of preparing a mixture for the manufacture of molds and rods on a gypsum binder is illustrated by the following example.

Example. Use the mixture of the composition of the prototype in the following ratio of ingredients, wt.%:
Gypsum - 14
Dinas - 60
Dusty sublimation of fireclay production - 4
Alumochromophosphate binder (AHFS) - 0.01
Water - the rest
When preparing the mixture, water is preliminarily mixed with AHPS and the resulting solution is poured into an ultrasonic bath. The dry molding material is poured into an aqueous solution of AHFS at the rate of 360 ... 380 ml of a saturator per 1 kg of dry components of the mixture. After mixing the mixture of ingredients, it is simultaneously subjected to vacuum and the application of an ultrasonic field. To do this, use the installation, which is a vacuum ultrasonic bath with an electric mixer. The bottom of the bath is a magnetostrictive transducer waveguide (PMS-15), connected in series to an electric circuit with an ultrasound generator of the brand UZG-22-10 / 4 /.

 The mixture is processed in such an apparatus at an ultrasound frequency of 22 kHz and a power output of 100 W at the generator output, while the amplitude of the vibration velocity of the waveguide surface is 0.06 m / s, and the residual air pressure in the ultrasonic bath is maintained within 1400 ... 2000 Pa. During the tests, the duration of the vacuum-ultrasonic treatment varies: 2, 4 and 6 minutes.

 In parallel to obtain comparative data, the mixture is prepared according to the prototype. Prepared mixtures are used for the manufacture of molds and cores with fixation of physical and mechanical properties.

 Indicators for comparison are the pore volume per 1 kg of molds at different heights of the flasks, the fluidity and duration of the hardening of the suspension on a gypsum binder with different degrees of filling, as well as the strength of the resulting molds and cores.

 The duration of the solidification of the mixture was fixed using a Vick needle / 5 /.

 The fluidity of the mixture was evaluated using the Suttard method, according to the diameter of the flow of 250 ml of the suspension when lifting a standard sleeve with the mixture on a gypsum binder, 8 minutes have passed from the moment of mixing / 5 /.

The strength of the molds was evaluated by testing for bending samples of size (40x20x5) · 10 ^-3 m after natural drying in air for 24 hours.

 The effect of vacuum-ultrasonic treatment of the mixture on the properties of molds and rods on a gypsum binder is presented in the table.

 From the table it is seen that used in the prototype method of vacuum treatment creates the conditions for the required degassing of gypsum slurry in the manufacture of only small castings. As the height of the flasks increases, the effectiveness of the method of preparing the mixture used and the prototype, significantly decreases. The degree of degassing of the mixture by the proposed vacuum-ultrasonic method is practically high for all the indicated dimensions of the flasks.

 The test results also show that, in comparison with the prototype, the claimed method for preparing the mixture provides its rheological properties necessary for the manufacture of castings. At the same time, reproducibility with a mixture of a thin-relief surface of models improves, the strength of molds and cores on a gypsum binder in the production of castings from non-ferrous and precious alloys increases almost 2.0 times.

 The method of preparation of the mixture was tested in the manufacture of large-sized art products and turbine wheels by investment casting, showing an improvement in the quality of these complex-shaped castings.

 Given the increased complex of the obtained technological properties, the claimed method of preparing a mixture for the manufacture of molds and cores on a gypsum binder can also be used to obtain complex casting equipment, in dental prosthetics, jewelry casting, and in the manufacture of critical engineering blanks.

List of references
1. Urvachev V.P., Kochetkov V.V., Gorina N.B. Lost and investment casting of copper alloys. - Chelyabinsk: Metallurgy, 1991 .-- 168 p.

 2. Magnitsky ON, Pirainen V.Yu. Art Casting - St. Petersburg: Polytechnic, 1996. - 213 p.

 3. RF patent N 2129932. A mixture for the manufacture of ceramic molds and cores in the manufacture of castings from non-ferrous and precious alloys and the method of its preparation / Znamensky LG, Kulakov BA, Krymsky VV et al. Bull. N 13, 1999 (prototype).

 4. Fundamentals of physics and technology of ultrasound / B.A. Agranat, M.N. Dubrovin, N.N. Khavsky and others. - M .: Higher school, 1987. - 352 p.

 5. Gutov L.A., Bablyak E.L., Isoiko A.P. Precious metal art casting. - L .: Engineering, 1988 .-- 224 p.

Claims (1)

 A method of preparing a mixture for the manufacture of molds and rods on a gypsum binder in the manufacture of castings from non-ferrous and precious alloys, including mixing the ingredients of the mixture and its vacuum treatment, characterized in that, simultaneously with the vacuum treatment, an ultrasonic field is applied to the mixture for 2-6 minutes.

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